1. Field of the Invention
The present invention relates to a machine for cleaning ballast excavated from a ballast bed supporting a track, the machine being movable on the track in an operating direction, which comprises two vertically and laterally adjustable endless excavating chains sequentially mounted in the operating direction on the machine and passing underneath the track for excavating the ballast, track lifting means on the machine, a screening installation for cleaning the excavated ballast, a conveyor arrangement for conveying the excavated ballast to the screening installation, and another conveyor arrangement for conveying the cleaned ballast from the screening installation to a ballast distributing device for distributing the cleaned ballast to the ballast bed. This invention is also directed to a novel bllast cleaning method.
2. Description of the Prior Art
Ballast cleaning machines of this type have been disclosed in published German paent application No. 43 43 148 A1, French patent No. 1,029,167 and German Democratic Republic patent No. 240 043. These machines have a machine frame supported on undercarriages at the ends of the machine frame for movement on the track in an operating direction, and two excavating chains are mounted on the machine frame immediately following each other in the operating direction. A ballast cleaning screening installation is arranged between the two ballast excavating chains. While the machine continuously advances along the track, the first excavating chain, as seen in the operating direction, excavates the ballast and conveys it to the screening installation, and the second, trailing excavating chain removes the soil underlying the ballast bed. The removed soil is conveyed to trailing storage cars. Before the cleaned ballast is distributed from the screening installation, a protective sand layer is laid on the subgrade.
French patent No. 714,645 shows an arrangement of four endless bucket chains for raising excavated ballast and convey it to a screening installation.
Another machine for rehabilitating a ballast bed is disclosed in European patent application No. 0 629 744 B1. A first excavating chain excavates a layer of ballast, and the excavated ballast is comminuted in a stone crusher. The comminuted ballast is distributed on the excavated ballast bed and compacted to serve as a protective layer over the subgrade. A second excavating chain mounted on a second machine frame removes soil, which is replaced by the protective layer, whereupon the track is laid. In a subsequent operating stage, new ballast is introduced to provide a ballast bed.
It is the primary object of this invention to provide a ballast cleaning machine of the first-described type and a ballast cleaning method to enhance the ballast cleaning efficiency.
The above and other objects are accomplished according to one aspect of the invention with a machine for cleaning ballast excavated from a ballast bed supporting a track, the machine being movable on the track in an operating direction, which comprises a first machine frame, and a second machine frame trailing the first machine frame in the operating direction and linked thereto, the ends of the machine frames being supported on the track by undercarriages. A first vertically and laterally adjustable endless excavating chain is mounted on the first machine frame and passes underneath the track for excavating the ballast, a first track lifting device is mounted on the first machine frame, a second vertically and laterally adjustable endless excavating chain is mounted on the second machine frame and passes underneath the track for excavating the ballast, and a second track lifting device is mounted on the second machine frame. The machine further comprises a screening installation for cleaning the excavated ballast, a first conveyor arrangement for conveying the excavated ballast from the first excavating chain to the screening installation, a second conveyor arrangement for conveying the excavated ballast from the second excavating chain to the screening installation, a ballast distributing device arranged at a trailing end of the second machine frame for distributing ballast cleaned on the screening installation to the ballast bed, and a third conveyor arrangement for conveying the cleaned ballast from the screening installation to the ballast distributing device, the third conveyor arrangement having a discharge end behind the second excavating chain in the operating direction and an inlet end arranged to receive the cleaned ballast from the screening installation.
According to another aspect, the present invention provides a method for cleaning ballast excavated from a ballast bed supporting a track, which comprises a first cleaning stage wherein an upper layer of the ballast bed is excavated, the excavated ballast is cleaned and the track is lowered to lay on the remaining layer of the ballast bed, a second and trailing cleaning stage immediately following the first cleaning stage, wherein the track is lifted, the ballast of the remaining layer of the ballast bed is excavated and the excavated ballast is cleaned, and the ballast cleaned in the first and second cleaning stages is distributed to the ballast bed before the track is lowered to lie on a cleaned ballast bed.
While the apparatus and method of this invention require a short temporary positioning of the track on an interim level of the excavated track, the ballast cleaning efficiency is considerably enhanced without requiring high constructural expenditures. Such high costs in constructing the machine would be involved if the two endless excavating chains were mounted on a common machine frame since the distance between the two undercarriages at the ends of such a common frame would have to be very large to permit a permissible flexing of the track. For this reason, the prior art preferred increasing the capacity of the screening installation and of the ballast excavating chains to obtain enhanced efficiency.
In a preferred embodiment, the ballast cleaning machine comprises vertically adjustable and vibratory ballast compacting devices for compacting the ballast at the shoulders of the ballast bed, the ballast compacting devices being mounted on the first machine frame at a rear end thereof where an undercarriage supports the machine frame on the track. In this way, the track position is temporarily stabilized during the short period of time before the cleaned ballast is distributed to the ballast bed so that the two undercarriages between the first and second ballast excavating chains may move on the track without problems.